As a conventional uniaxial eccentric screw pump of this type, the uniaxial eccentric screw pump described in JP Publication No. 59-153992 is known. That uniaxial eccentric screw pump is provided with a male-threaded rotor directly coupled to a driving shaft and a stator rotatably supported by a housing via bearings. A female-threaded inner surface has its rotational axial line eccentrically arranged with respect to a rotational axial line of the rotor. The rotor pumps the fluid from the intake side to the discharge side, while rotating and by eccentrically moving with respect to the rotational axial line of the stator.
Specifically, in the uniaxial eccentric screw pump described in JP Publication No. 59-153992, in which the stator is rotatably supported by the housing via the bearings, in order to prevent the fluid taken in on the intake side from entering between the housing and the stator and to prevent the fluid from entering between the housing and the stator from the discharge side, a seal member is provided between the secured housing, and an intake side end portion of the rotating stator and a discharge side end portion thereof to seal between the housing and the stator.
FIG. 6 shows an example of a uniaxial eccentric screw pump of this type, in which seal member is arranged between the housing and the intake side end portion of the stator and between the housing and the discharge side end portion of the stator.
A uniaxial eccentric screw pump 101 shown in FIG. 6 has a frame 111 for accommodating a driving shaft 102 coupled to a motor (not shown). The driving shaft 102 is rotatably supported by the frame 111 via bearings 116.
The frame 111 is attached to a housing 110. The housing 110 is provided with, sequentially from the intake side (from the right side of FIG. 6): an intake portion 110a; a main portion 110b; and a discharge portion 110c. The intake portion 110a of the housing 110 is formed with an inlet 112 for the fluid to be pumped, and the discharge portion 110c is formed with an outlet 113 for the pumped fluid.
Then, the uniaxial eccentric screw pump 101 is provided in the housing 110 with a male-threaded rotor 103 and a stator 104 having a female-threaded inner surface.
The rotor 103 is constituted by a helical portion 103a on the front end side and a base end portion 103b on the back end side. The base end portion 103b linearly extends in the frame 111 and is coupled to the driving shaft 102 without a use of a universal joint. The base end portion 103b of the rotor 103 is coupled to the driving shaft 102, and rotates together with the driving shaft 102. On the other hand, the helical portion 103a has an elliptical cross-section eccentric with respect to the rotational axial line of itself, and the helical portion 3a is internally provided in the stator 104 having a female-threaded inner surface.
The rotational axis of the rotor 103 is arranged to be eccentric by a predefined eccentric amount with respect to the rotational axial line of the stator 104.
Both ends of the stator 104 are rotatably supported by the housing 110 via a pair of bearings 105 and 106. The bearing 105 of the pair of bearings 105 and 106 is a self-lubricating bearing, and is arranged on the discharge side of the stator 104. On the other hand, the bearing 106 is a self-lubricating bearing, and is arranged on the intake side of the stator 104. The bearing 105 is directly attached to the main portion 110b of the housing 110, whereas the bearing 106 is attached to the intake portion 110a and the main portion 110b of the housing 110 via a bearing housing 107. The rotation of the bearing housing 107 is stopped by a key member 108.
In addition, the stator 104 is constituted by a metallic outer stator cylinder 104a and a rubber inner stator cylinder 104b arranged in the metallic outer stator cylinder 104a. The rubber inner stator cylinder 104b is formed with a helical female screw hole having an elliptical cross-sectional shape with a double pitch of the helical portion 103a of the rotor 103.
As a stator seal structure, in order to prevent the fluid taken in from the inlet 112 from entering between the housing 110 and the stator 104, a lip seal 114 is provided between the housing 110 and the intake side end portion of the stator 104. In order to prevent the fluid from entering between the housing 110 and the stator 104 from the outlet 113, a lip seal 115 is provided between the housing 110 and the discharge side end portion of the stator 104. The lip seals 114 and 115 are made from Teflon® or rubber for sealing spaces between the housing 110 and the stator 104.
Specifically, a mechanical seal 120 is provided between the base end portion 103b of the rotor 103 and is coupled to the driving shaft 102 and the frame 111. The mechanical seal 120 has a function of blocking the pumped fluid flown in from the inlet 112 from flowing into the frame 111 through a gap between the base end portion 103b and the frame 111.
The mechanical seal 120 is provided with: a rotating ring 121 arranged around the base end portion 103b and a secured ring 122 arranged to be opposite to the rotating ring 121 in a rotational axial line direction of the base end portion 103b and secured to the frame 111. A flange member 124 is secured by a securing pin 125 around the base end portion 103b on the helical portion 103a side rather than the rotating ring 121 side. A spring 123, for biasing the rotating ring 121 in a direction toward the secured ring 122 and pressing the rotating ring 121 against the secured ring 122, is arranged between the flange member 124 and the rotating ring 121. This causes a sliding seal surface of the rotating ring 121 and a sliding seal surface of the secured ring 122 to contact with each other slidably in a circumferential direction, thereby ensuring a predefined contact pressure to seal space between the rotating ring 121 and the secured ring 122.